American Airlines, British Airways and Spain’s Iberia, which are seeking regulatory approval to forge a transcontinental venture, have challenged rivals’ claims that the alliance would dominate key routes between the US and London.

American, BA and Iberia aim to persuade US officials to grant their venture immunity from antitrust rules that limit their ability to co-ordinate schedules and fares, and share revenue. The planned alliance drew fire from Virgin, run by Sir Richard Branson.